Vista's new interface design and security enhancements have become productivity degrader and make your day to day computing experience quite painful. These issues together with increased computer hardware requirements make Windows Vista less than ideal for day to day usage.
PC World has termed Vista as the #1 of 15 biggest technology disappointments of 2007.
If you are planning to move to this latest and greatest version of Microsoft Windows, stop and think before you jump.
Sticking to Windows XP for the time being seems the best choice available. Windows XP is going to be supported with bug fixes till April 8, 2014. By that time, we hope Vista will turn into something better or we might have other better choices.
So if you do not have any particular requirement to install Windows Vista (you don't have if you don't know), stick to Windows XP. Your computer will run familiar, faster and cheaper.